ipc: Create an unforgeable mechanism to get the process id of the sender.

ipc/ipc_channel_reader.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ipc/ipc_channel_reader.h"
 
 #include <algorithm>
 
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_logging.h"
@@ skipping 132 matching lines @@
       return DISPATCH_WAITING_ON_BROKER;
     }
 
     DispatchMessage(m);
     queued_messages_.erase(queued_messages_.begin());
   }
   return DISPATCH_FINISHED;
 }
 
 void ChannelReader::DispatchMessage(Message* m) {
+  m->set_sender_pid(GetSenderPID());
+
 #ifdef IPC_MESSAGE_LOG_ENABLED
   std::string name;
   Logging::GetInstance()->GetMessageText(m->type(), &name, m, NULL);
   TRACE_EVENT1("ipc,toplevel", "ChannelReader::DispatchInputData", "name",
                name);
 #else
   TRACE_EVENT2("ipc,toplevel", "ChannelReader::DispatchInputData", "class",
                IPC_MESSAGE_ID_CLASS(m->type()), "line",
                IPC_MESSAGE_ID_LINE(m->type()));
 #endif
@@ skipping 54 matching lines @@
 }
 
 void ChannelReader::StopObservingAttachmentBroker() {
 #if USE_ATTACHMENT_BROKER
   GetAttachmentBroker()->RemoveObserver(this);
 #endif  // USE_ATTACHMENT_BROKER
 }
 
 }  // namespace internal
 }  // namespace IPC